1. Field of the Invention
The present invention relates to an apparatus that starts an internal combustion engine that is linked with a rotating shaft of a motor via a damper, a starting control method, and a starting control apparatus for a hybrid vehicle with an internal combustion engine and a motor mounted thereon.
2. Description of the Related Art
A typical structure to start an internal combustion engine mounted on a vehicle cranks the internal combustion engine with a self-starting motor, which is specifically used for starting and linked with a rotating shaft of the internal combustion engine, and simultaneously feeds a supply of fuel. The self-starting motor is a small-sized motor for starting the internal combustion engine and enables the internal combustion engine to be rotated only to a significantly lower revolving speed (several hundred rpm) than an idle speed. The internal combustion engine is driven to a certain level of revolving speed that enables subsequent self starting and driving, through combustion of the supplied fuel.
In a hybrid vehicle which has an internal combustion engine and a motor mounted thereon and outputs a power for driving at least from the motor, some proposed systems do not have a self-starting motor specifically used for starting but uses a motor that is linked with a rotating shaft of an internal combustion engine to start the internal combustion engine (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 6-144020 and No. 9-222064. In this system, the rotating shaft of the internal combustion engine is linked with a rotating shaft of a first motor via a first clutch, whereas the rotating shaft of the first motor is connected via a second clutch with a drive shaft that is mechanically linked with wheels. A second motor is further connected to the drive shaft. At the time of starting the internal combustion engine, while the first clutch is engaged and the second clutch is released, the first motor cranks or motors the internal combustion engine prior to a supply of fuel. When the revolving speed of the internal combustion engine becomes equal to or greater than a preset value, the supply of fuel is fed to the internal combustion engine, which subsequently starts through the compression and combustion of the air/fuel mixture. After the start of the internal combustion engine, the first motor is driven as a generator with the power output from the internal combustion engine to charge the battery or to output the power directly to the drive shaft and drive the vehicle while the second clutch is engaged.
In the conventional starting control apparatus for the hybrid vehicle, however, a large load is applied to the battery. The battery is exposed to an excessive load especially when the internal combustion engine has poor startability. This is ascribed to the following reasons:
(1) In the hybrid vehicle, the motor is larger in size than the conventional self-starting motor and consumes a greater amount of electric power;
(2) In the hybrid vehicle, the rotor of the motor, which has a significantly larger mass than that of the self-starting motor, is connected to the rotating shaft of the engine. This often causes torsional resonance. A large torque is output from the motor, in order to enable the revolving speed of the internal combustion engine to quickly pass through the range of possible torsional resonance. This increases the electric power consumed by the motor.
(3) In the hybrid vehicle, the motor can increase the revolving speed of the internal combustion engine to a higher level than that in the conventional vehicle. The supply of fuel to the internal combustion engine and the combustion of the air/fuel mixture accordingly start at the higher revolving speed, since the start of combustion at the higher revolving speed improves the emission. The increase in revolving speed of the internal combustion engine to the higher level, however, increases the amount of electric power consumed by the motor.
Among these problems, (2) and (3) are not negligible especially when the internal combustion engine is cold. When the internal combustion engine is cold, the high viscosity of lubricant causes the revolving speed of the internal combustion engine not to quickly increase, in response to supply of electric current to allow output of a large torque from the motor. A large electric power is accordingly consumed before the revolving speed reaches a preset level (for example, 800 rpm). The problems (1) through (3) are not only observed in the hybrid vehicle but in any other structures that use a large-sized self-starting motor.
One proposed countermeasure uniformly limits the supply of electricity from the battery according to the elapse of time (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 63-297767). This uniform limitation is, however, not practical, since a little more continuance of cranking may start the internal combustion engine. Especially in the case of the large-sized self-starting motor, one cranking operation consumes a large amount of electric power. Several tries of starting with limitation of the cranking time cause the battery to be exposed to a greater load.
The object of the present invention is to start an internal combustion engine without causing a battery to be exposed to an excessive load even when the internal combustion engine is cold.
The present invention realizes at least part of the above and the other related objects, based on the following two principles. The first principle is that the output torque of the motor for rotating the internal combustion engine is restricted to a smaller value in response to the lower startability of the internal combustion engine. The second principle is that the supply of electricity is restricted when the output torque of the motor does not have a negative value during a starting control operation. These principles are favorably applicable to the internal combustion engine having a starting motor, as the starting control apparatus for the internal combustion engine or the method of starting the internal combustion engine especially in the hybrid vehicle, as discussed below.
The present invention is directed to a first starting control apparatus for an internal combustion engine that rotates the internal combustion engine, which is connected via a damper with a rotating shaft of a motor driven by a battery, with the motor so as to start the internal combustion engine. The first starting control apparatus includes: a startability detection unit that detects a parameter relating to startability of the internal combustion engine; and an output torque restriction unit that restricts an output torque of the motor for rotating the internal combustion engine to a smaller value, in response to lower startability of the internal combustion engine specified from the parameter detected by the internal combustion engine startability detection unit.
The present invention is also directed to a first method of starting an internal combustion engine, which corresponds to the first starting control apparatus. The first method rotates an internal combustion engine, which is connected via a damper with a rotating shaft of a motor driven by a battery, with the motor so as to start the internal combustion engine. The first method includes the steps of: (a) detecting a parameter relating to startability of the internal combustion engine: and (b) restricting an output torque of the motor for rotating the internal combustion engine to a smaller value, in response to lower startability of the internal combustion engine specified from the parameter detected in the step (a).
In the first starting control apparatus for the internal combustion engine and the corresponding first method, in response to the lower startability of the internal combustion engine, the output torque of the motor for rotating the internal combustion engine is restricted to a smaller value. This arrangement effectively prevents the electric power from being wasted when the internal combustion engine has poor startability and the revolving speed of the internal combustion engine is not quickly increased by application of the torque from the motor.
It is preferable that the supply of fuel to the internal combustion engine starts at the lower revolving speed in response to the lower startability of the internal combustion engine. This arrangement effectively prevents the motor from being driven over a long time period prior to a start of the fuel supply and excessively consuming the electric power of the battery. The internal combustion engine that receives the supply of fuel tries self rotation through the combustion of the air/fuel ratio. In the state of full combustion, the internal combustion engine starts self driving.
In the first starting control apparatus for the internal combustion engine and the corresponding first method, the parameter relating to the startability of the internal combustion engine may be a temperature of the internal combustion engine. The startability of the internal combustion engine is affected by the adhesion of the supplied fuel to an intake port or the viscosity of lubricant, so that the temperature of the internal combustion engine is a preferable parameter relating to the startability of the internal combustion engine. The cooling water temperature, the temperature of lubricant, or the intake air temperature may be used as the temperature of the internal combustion engine.
In accordance with one preferable application, the first starting control apparatus further includes: a full combustion determination unit for determining that the internal combustion engine is in a state of full combustion, based on a driving condition of the internal combustion engine; a time count unit for determining that a predetermined time period has elapsed since a start of cranking the internal combustion engine by the motor; and a starting control discontinuance unit that cuts off a supply of electricity from the battery to the motor and once stops starting control of the internal combustion engine, when the full combustion determination unit determines that the internal combustion engine is not in the state of full combustion while the time count unit determines that the predetermined time period has elapsed.
The starting control apparatus of this preferable structure determines that the internal combustion engine is in the state of full combustion, and cuts off the supply of electricity from the battery to the motor and stops the starting control of the internal combustion engine, when the internal combustion engine does not fall into the state of full combustion within the predetermined time period. This arrangement effectively prevents the electric power of the battery from being consumed over a long time period without causing the internal combustion engine to fall into the state of full combustion.
In accordance with one preferable structure, the full combustion determination unit includes a torque measuring unit that measures an actual output torque of the motor as the driving condition of the internal combustion engine. The full combustion determination unit determines that the internal combustion engine is in the state of full combustion when the actual output torque measured by the torque detection unit has a negative value. The output torque of the motor is regulated at the time of starting the internal combustion engine. The measurement of the actual output torque thus assures the determination of whether or not the internal combustion engine is in the state of full combustion.
In the starting control apparatus that carries out the full combustion determination, it is preferable that a greater value is set to the predetermined time period, which is a target of the determination by the time count unit, in response to the lower startability of the internal combustion engine specified from the parameter. As is known, the lower startability results in extending the time period required for the full combustion. In this case, the uniform discontinuance of the starting control after the elapse of the preset time period may cause the electric power of the battery to be wastefully consumed. This preferable arrangement extends the time period for the full combustion determination in the case of the lower startability, thereby enabling the accurate and efficient determination of starting the internal combustion engine. The predetermined time period for the full combustion determination may be based on the time or the integrated revolving speed of the internal combustion engine.
Another preferable structure estimates an amount of electric power suppliable from the battery and sets a greater value to the predetermined time period, which is a target of the determination by the time count unit, for the greater amount of estimated electric power. When it is assumed that the large electric power is suppliable from the battery, the time period for stating control is extended. The starting control can be continued in the case where the suppliable electric power is sufficient. This arrangement effectively prevents the supply of electricity from the battery from being cut off while a little more continuance causes the internal combustion engine to fall into the state of full combustion. This prevents the electric power from being wasted.
The electric power suppliable from the battery is generally estimated in the process of control of the battery. Another available technique measures the suppliable electric power directly. Still another available technique measures the temperature of the battery and corrects the estimated value of suppliable electric power to a higher value at the higher observed temperature.
Still another preferable structure integrates electric power consumed by the battery since the start of cranking and determines that the predetermined time period has elapsed when the integrated electric power reaches a preset reference value. This structure enables the electric power of the battery to be efficiently used for cranking without causing excessive discharge.
In this case, one preferable structure measures the temperature of the battery, and corrects the preset reference value, which is used for the full combustion determination, to a smaller value at the lower observed battery temperature. When a decrease in performance of the battery is expected, for example, when the vehicle is cold, the full combustion determination is carried out at an earlier timing. This arrangement discontinues the consumption of electric power when the internal combustion engine is not in the state of full combustion. This prevents the battery from being exposed to the excessive loading.
Another preferable application of the first starting control apparatus adjusts an open-close timing of an air intake valve of the internal combustion engine, in order to lower an effective compression ratio of the internal combustion engine, at a time of starting the internal combustion engine. The decrease in effective compression ratio decreases the loading seen from the motor and enables the revolving speed of the internal combustion engine to quickly increase.
The starting control apparatus for the internal combustion engine is applicable to the conventional structure that starts the internal combustion engine with a self-starting motor, but is especially effective in the hybrid vehicle where the motor, which adds a torque to the output of the internal combustion engine and regenerates electric power from the output of the internal combustion engine or the braking force, is attached to the output shaft of the internal combustion engine. In the hybrid vehicle, it is required to quickly increase the revolving speed of the internal combustion engine at the time of starting the internal combustion engine, because of the possibility of torsional resonance, as described below.
The crankshaft or output shaft of the internal combustion engine is generally a resilient body, which has a mass distribution, and thereby forms a vibrational system of infinite degree of freedom. A torque variation due to the combustion or the reciprocating motions of the piston causes torsional vibrations. When the natural frequency and the forced frequency of the axis coincide with each other, torsional resonance occurs. An increase in amplitude of the torsional vibration causes a foreign noise or wear of the gear in the crankshaft system and, in some cases, a fatigue of the crankshaft. The torsional resonance often occurs when the revolving speed of the crankshaft is less than an idle speed. In the apparatus that motors the internal combustion engine with the motor that is connected to the crankshaft of the internal combustion engine via a damper, the torsional resonance accordingly occurs at the time of starting the internal combustion engine.
In the hybrid vehicle where the torsional resonance often occurs, the high torque is output from the motor, in order to enable the revolving speed of the internal combustion engine to quickly pass through the range of possible torsional resonance at the time of starting the internal combustion engine. This causes the large power consumption of the battery. The above structures accordingly have significant effects on prevention of wasteful power consumption.
As described above, there is a unique problem in the hybrid vehicle where the motor, which adds a torque to the output of the internal combustion engine and regenerates electric power from the output of the internal combustion engine or the braking force, is attached to the output shaft of the internal combustion engine. The present invention is accordingly directed to a second starting control apparatus that starts an internal combustion engine with a motor, in a hybrid vehicle having the internal combustion engine, which is connected via a damper with a rotating shaft of the motor driven by a battery. The second starting control apparatus includes: a torque control unit that controls an output torque of the motor, based on a relationship between an output torque of the internal combustion engine and a torque required for the drive shaft; a torque detection unit for detecting that the output torque of the motor has a negative value; and an supply of electricity limiting unit that causes the torque detection unit to carry out the determination while the motor cranks the internal combustion engine, and limits a supply of electricity from a battery to the motor when the output torque of the motor does not have a negative value.
The present invention is also directed to a second method of starting an internal combustion engine, which corresponds to the second starting control apparatus. In a hybrid vehicle having an internal combustion engine, which is connected via a damper with a rotating shaft of a motor driven by a battery, the second method rotates the internal combustion engine with the motor so as to start the internal combustion engine. The second method includes the steps of: controlling an output torque of the motor, based on a relationship between an output torque of the internal combustion engine and a torque required for the drive shaft; determining that the output torque of the motor has a negative value while the motor cranks the internal combustion engine; and cutting off a supply of electricity from a battery to the motor when the output torque of the motor does not have a negative value.
In the second starting control apparatus and the corresponding second method, it is determined whether or not the output torque of the motor has a negative value. In the case where the output torque does not have a negative value, it is determined that the internal combustion engine has not started yet, and the supply of electricity to the motor is restricted. This structure readily and accurately carries out the full combustion determination based on the output torque of the motor, thereby ensuring the appropriate starting control without causing the battery to be exposed to the excessive loading.
In accordance with one preferable application, the second starting control apparatus further includes a time count unit for determining that a predetermined time period has elapsed since a start of cranking the internal combustion engine by the motor, wherein the supply of electricity limiting unit causes the torque detection unit to carry out the determination at a specific time point when the time count unit determines that the predetermined time period has elapsed, and cuts off a supply of electricity from the battery to the motor, so as to stop the cranking of the internal combustion engine, when the output torque of the motor does not have a negative value at the specific time point.
This arrangement enables the full combustion determination to be carried out at a desired timing. When the output torque of the motor does not have a negative value, this structure cuts off the supply of electricity and thereby prevents the battery from being exposed to the excessive loading.
The preferable structures of the first starting control apparatus discussed above are also applicable to the second starting control apparatus. One possible structure detects a parameter relating to the startability of the internal combustion engine and adjusts the predetermined time period for the full combustion determination. Another possible structure estimates the electric power suppliable from the battery and extends the predetermined time period based on the estimated value. It is also preferable to correct the estimated value of suppliable electric power to a higher value at the higher observed battery temperature.
Still another possible structure integrates electric power consumed by the battery since the start of cranking and determines that the predetermined time period for full combustion determination has elapsed when the integrated electric power reaches a preset reference value. In this structure, it is preferable that the preset reference value is specified by taking into account the battery temperature.
Another preferable application of the second starting control apparatus adjusts the open-close timing of the air intake valve of the internal combustion engine, in order to lower the effective compression ratio of the internal combustion engine, at the time of starting the internal combustion engine.
The first starting control apparatus for the internal combustion engine is applicable to the hybrid vehicle. The present invention is accordingly directed to a first starting control apparatus for a hybrid vehicle, which starts an internal combustion engine in a hybrid vehicle that takes out power of the internal combustion engine in an electrical form and outputs power of a motor at least to a drive shaft of the vehicle. The first starting control apparatus for the hybrid vehicle includes: a motor that cranks the internal combustion engine at a start of the internal combustion engine; a starting-time fuel supply unit that controls a supply of fuel to the internal combustion engine, simultaneously with cranking of the internal combustion engine by the motor; a startability detection unit that detects a parameter relating to startability of the internal combustion engine; and an output torque restriction unit that restricts an output torque of the motor for rotating the internal combustion engine to a smaller value at the time of cranking, in response to lower startability of the internal combustion engine specified from the parameter detected by the internal combustion engine startability detection unit.
The present invention is further directed to a second starting control apparatus for a hybrid vehicle, which corresponds to the second starting control apparatus for the internal combustion engine. The second starting control apparatus starts an internal combustion engine in a hybrid vehicle that takes out power of the internal combustion engine in an electrical form and outputs power of a motor at least to a drive shaft of the vehicle. The second starting control apparatus includes: the motor that cranks the internal combustion engine at a start of the internal combustion engine; a starting-time fuel supply unit that controls a supply of fuel to the internal combustion engine, simultaneously with cranking of the internal combustion engine by the motor; a torque control unit that controls-an output torque of the motor, based on a relationship between an output torque of the internal combustion engine and a torque required for the drive shaft; a torque detection unit for detecting that the output torque of the motor has a negative value; and an electricity cut-off unit that causes the torque detection unit to carry out the determination while the motor cranks the internal combustion engine, and cuts off a supply of electricity from a battery to the motor when the output torque of the motor does not have a negative value.
These apparatuses can start the internal combustion engine in the hybrid vehicle without causing the battery to be exposed to an excessive load.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.